Example of determination of the nitrogen abundance and v_trub for star AV47. The horizontal axis shows the wavelengths of the different nitrogen lines used, labelled by their wavelength. The vertical axis gives the best fitting abundance (N/H by number) for each line. Different symbols and colours correspond to different microturbulent velocities. All points for line N III 3355 overlap. The grey line and area highlight the final abundance value and its uncertainty. See text for discussion.